The present invention relates to a system and method for monitoring underground storage tanks, and, more particularly, to such a system and method in which a number of underground fuel storage tanks, such as in gasoline service stations spread over a wide geographic area, are all monitored from a central location.
Recent environmental concerns with underground fuel storage tanks have led the Environmental Protection Agency to create strict monitoring rules for gasoline service stations and other users of such tanks. Compliance with these regulations, which can require accuracy within xe2x85x9 inch of liquid level and must detect leakage rates of as little as 0.1 gal/hr. or less, can be an expensive and time consuming activity for a small business such as a service station. In an effort to alleviate this burden, a number of companies have developed systems for monitoring underground storage tanks for leakage compliance. In addition, some of these systems use the data collected for inventory management services as well. Examples of leak detection systems are found in U.S. Pat. No. 4,852,054 to John Mastrandrea; U.S. Pat. No. 5,075,877 to Allan Jacob; U.S. Pat. No. 5,297,423 to Jerome Keating, et al.; U.S. Pat. No. 5,363,093 to Barry Williams et al.; U.S. Pat. No. 5,400,253 to Paul O""Connor: U.S. Pat. No. 5,471,867 to John Tuma et al.; and U.S. Pat. No. 5,757,664 to Warren Rogers, et al. These prior art systems all require complex liquid level sensors which are hardwired to monitoring computers on site. This presents a number of problems. Typically, installation of such liquid level sensors requires the tank top to be accessed, which means tearing up concrete or asphalt surfaces covering the tank. The cables connecting the liquid level sensors to the monitoring computer are usually run beneath the road surface, which also requires the concrete or asphalt to be cut. Such probes usually must be installed in risers other than the fill riser, which can require expensive tank modifications. Many prior art systems require the installation of additional sensors such as temperature and/or pressure probes to detect fuel temperature and internal tank pressure as variables in computing liquid volume. Finally, many prior art centralized systems require a dedicated telephone line from service station to central monitoring computer, which also adds to the expense.
It is clear, then, that an improved underground storage tank monitoring system and method is needed. Such a system and method should avoid the above-mentioned problems of the prior art and should provide reliable monitoring at an economical price.
The present invention is an underground storage tank monitoring system and method which uses a special micropower impulse radar transmitter/receiver as a liquid level probe. Technical details for the micropower impulse radar probes are found in U.S. Pat. No. 5,609,059, entitled xe2x80x9cElectronic Multi-Purpose Material Level Sensorxe2x80x9d and U.S. Pat. No. 5,610,611, entitled xe2x80x9cHigh Accuracy Electronic Materials Level Sensorxe2x80x9d, which patents are incorporated herein by reference. One such probe is inserted into each storage tank, either through a dedicated monitor riser or, if none is available, in the existing fill riser via a special installation technique. The micropower impulse radar probes use flexible waveguides which extend downward to the tank bottom and which allow micropower radar impulses from the probe to travel down the waveguide, to reflect off of the liquid surface, and to return to the probe. The time lapse between emission and reception of the impulse by the micropower impulse radar probe is measured and a distance to the liquid surface, and thus a liquid level, can be calculated therefrom. In addition, a portion of each impulse travels through the fuel and is secondarily reflected off of the surface of any water which has accumulated in the tank. In this manner, a water level can also be calculated from the time between impulse transmission and reception of these secondary impulses. Each micropower impulse radar probe is connected to a dedicated, low power, spread spectrum transmitter which collects level and status information from the probe, encodes and transmits it to a matching spread spectrum receiver nearby, preferably within the service station building. The receiver converts the coded signals into electrical signals and forwards them to a processor, to which is connected a modem and a back-up battery power source. The processor stores the liquid level information, including fuel level and, optionally, accumulated water level, for later transmission to a central monitoring site via the modem. A data entry keyboard is also provided for entering fuel dispensed and fuel displaced information into the processor. Unlike many other systems which periodically poll the service station from the central monitoring site, the inventive system does not require a dedicated telephone line for implementation since the data transmission is initiated from the service station only during regular reporting times or when an abnormal condition occurs.
The objects and advantages of the invention include: providing an underground storage tank monitoring system and method; providing such an underground storage tank monitoring system and method in which a number of different underground storage tanks can be monitored efficiently from a central monitoring site; providing such an underground storage tank monitoring system and method in which a micropower impulse radar probe is inserted into each tank via a riser, connected to a spread spectrum transmitter positioned in a manhole containing the riser, which transmitter transmits liquid level information to a remote receiver; providing such an underground storage tank monitoring system and method in which a special installation system allows the micropower impulse radar probes to be inserted via the fill riser of an existing tank where no monitor riser is available; providing such an underground storage tank monitoring system and method which uses liquid levels, as measured by the micropower impulse radar probes, along with quantities of fuel dispensed from the tank and fuel replaced in the tank to calculate leak rates, and, optionally, perform inventory control; providing such an underground storage tank monitoring system and method which is particularly economical to install and implement as compared to existing systems; and providing such an underground storage tank monitoring,,system and method which is particularly well suited for its intended purpose.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.